The present invention relates to an MR (magnetic resonance) imaging system and method, and more particularly to an MR imaging system and method using a surface coil.
An MR imaging system is known as a medical apparatus for acquiring a cross-sectional image of an object to be examined such as a human body. However, there may be the case where the acquisition of a tomographic image of a local portion of the object in an arbitrary direction is desired without the need of the cross-sectional image of the object. A surface coil has been proposed in order to satisfy such a requirement. The surface coil is used together with three-dimensional orthogonal field gradient coils incorporated into an MR imaging system and serves to generate a high frequency or RF magnetic field and to detect a magnetic resonance signal. The surface coil is used in contact with a local portion of an object to be examined a tomographic image of which is to be acquired.
When a high frequency magnetic field having a predetermined intensity is generated by use of the surface coil, the intensity of a magnetic resonance signal changes in accordance with a distance from a surface of the object to be examined since the flip angle of nuclear spins is different depending on the distance from the surface of the object to be examined. Accordingly, in the case where it is desired to acquire a tomographic image of a plane parallel to a coil plane of the surface coil, a magnetic resonance signal can be detected with the maximum intensity by optimizing a high frequency magnetic field generating signal to be inputted to the surface coil. In the prior art, however, no sufficient consideration is paid to such an aspect. Even if any consideration is involved, there is a problem that the construction becomes complicated, for example, an additional surface coil is required (see JP-A-62-26053).